"We will also be hearing directly from asylum seekers within the facilities because we know that long-term detention is having a significant impact on the mental health and wellbeing of these people," she said.

"Levels of self-harm in the Darwin facilities are extremely high and it is because people have been detained for far too long."

Senator Hanson-Young says a new 1,500 bed detention centre being built on the outskirts of Darwin is a waste of taxpayers' money.

The Federal Government is spending $74 million to lease a site site at Wickham Point over three years, as well as millions more to run the facility.

Senator Sarah Hanson-Young says the money could be better spent.

"We should be facilitating community based assessment, which saves Australian taxpayers money and it keeps intact the mental health and wellbeing of these very vulnerable people, she said."

At today's hearing, an Australian Medical Association representative told the inquiry the federal government is engaging in child abuse by detaining children and families for long periods.

Doctor Peter Morris, from the Northern Territory branch of the AMA, told the committee that medical staff in Darwin are having to deal with regular avoidable self-harming by children.

One child who came to Royal Darwin Hospital after attempting suicide was aged nine.

Mr Morris says the system of indefinite mandatory detention of asylum seekers violates human rights, is a form of child abuse and wastes money.

The AMA has given the committee five recommendations, including that children and families should be detained for just three days for initial security and health checks before being released into the community while their claims are being assessed.

An asylum seeker support group told the inquiry that long mandatory detention is leading to domestic violence within asylum seeker families.

Four Darwin asylum seeker support network volunteers told the committee they have been co-ordinating a detention centre visiting program.

Adriene Walters from the group said prolonged detention is putting stress on relationships and causing domestic violence.

She said she was concerned SERCO, which staffs and operates the Darwin detention centre, was relying on reporting domestic violence to police rather than taking any action to stop it, such as moving asylum seekers to other centres.

Ms Walters says asylum seekers are being brought before the courts on domestic violence charges without any legal advice and without any advice as to how it might affect their refugee claims.Northern Territory Police told the inquiry that responding to violence and unrest in Darwin's detention centres is compromising their other work.